#include <fstream>
using namespace std;

ifstream in("branza.in");
ofstream out("branza.out");

int v[100000],dq[100000];
long long n,s,t,p,suma=0;

int main()
{
   in>>n>>s>>t;
   t++;
   int st=0,dr=-1;
   for(int i=0;i<n;i++){
    in>>v[i]>>p;
    if(i>=t && dq[st]==i-t){
    st++;
    }
    while(st<=dr && v[i] && v[i]<=v[dq[dr]]+(i-dq[dr])*s){
    dr--;
    }
    dq[++dr]=i;
        suma+=p*(v[dq[st]]+(i-dq[st])*s);
   }
   out<<suma;

    return 0;

}